Wireless communication has enjoyed explosive growth over the past decade. As demands for increased capacity and quality grow, improved methods for harnessing the multipath wireless channel must be developed. The use of adaptive antenna arrays is one area that shows promise for improving capacity of wireless systems and providing improved safety through position location capabilities. These arrays can be used for interference rejection through spatial filtering, position location through direction finding measurements, and developing improved channel models through angle of arrival channel sounding measurements. This thesis provides an overview of the technical challenges involved in position location of wireless users and details the hardware development of a multi-sensor testbed at the Mobile and Portable Radio Research Group at Virginia Tech. This testbed is to be used for position location experiments as well as a host of other adaptive signal processing applications. / Master of Science

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The desire to counter multipath effects and improve communication links between mobile wireless systems in dense environment has led to much research in implementing antenna diversity. Space diversity, utilizing two or more antennas separated several wavelengths from one another, is one of the most popular method to achieve this operation. Meanwhile, polarization diversity, utilizing two orthogonal polarizations, has become more attractive in reducing cost and size of antenna systems. Polarization diversity is achieved using two orthogonal feeds to excite the two orthogonal polarization planes of the antenna. The challenge associated with designing dual polarized antennas is the need to reduce isolation between the feed and cross polarization level while maintaining a high efficiency. While a number of studies are successful in realizing polarization diversity, their antenna structure typically present more complex structures involving multiple layers. This thesis presents a novel method to implement polarization diversity on a miniature antenna using a simple planar structure. The antenna structure uses two crossed slots further miniaturized using a method derived from a recent study on miniaturized spiral slot antenna. At an operating frequency of ~ 1 GHz, the antenna is capable of achieving efficiency greater than 90% with a size as small as 0.08 .? x 0.08? The dual polarization operation is achieved by exciting the magnetic currents of the crossed slots with two orthogonal coplanar waveguide feeds. Simulation results of the proposed antenna yield an isolation > 15 dB with cross polarization levels > 10 dB. Theantenna structure was designed using CST Microwave Studio and the simulations were performed using IE3D simulation software.

Approved for public release; distribution is unlimited / The Linearly Tapered Slot Antenna (LTSA) had been investigated and developed experimentally; its applications have primarily been based on empirical designs. An accurate theoretical model based on Moment Methods (MM) is developed here to study the radiation characteristics of the LTSA. Using the MM solutions to the reaction integral equation, this thesis presents an analysis to model and explain the LTSA behavior. The effects of variable design parameters on radiation patterns are studied. Discussion is augmented by relating predicted radiation patterns to calculated current distributions on the antenna surface. Conclusions are made regarding optimum designs for the LTSA. Relevant observations are made concerning the extensive computational tasks and the computer resources required for the MM model. / http://archive.org/details/modelingbehavior00kell / Major, United States Army

This thesis presents a novel antenna structure that satisfies the challenging requirements of an air coupled high speed ground penetrating radar (GPR). The desired GPR system is to achieve high spatial resolution and accurate inspection results while scanning at relatively high speed for highway pavement and bridge deck inspection. This work utilizes the Ultra Wide Band (UWB) antenna design to achieve both physical and electrical requirements imposed. The design procedure starts with a short survey to discuss typical UWB antennas used for GPR applications, and various tradeoffs of each type specifically when used for Air Coupled GPR applications. Our structure anatomy is presented, followed by a theory introduction that mainly focuses on achieving good impedance matching throughout the proposed antenna structure. A proof-of-concept MATLAB model is created to evaluate the preliminary physical dimensions that can achieve minimum reflections at antenna's feed point. These dimensions are then used in SolidWorks to create a 3D model that is imported later in HFSS to obtain accurate electromagnetic characteristics. Furthermore, fine tunings are performed to the antenna structure to optimize both gain and impedance matching. The SolidWorks 3-D structural model is finally used for antenna fabrication. The measurements recorded from the field experiments using the prototypes manufactured are compared to the simulation results confirming our initial findings. Both measurements and simulation results demonstrated very small reflection loss across the 700 MHz ~ 6 GHz frequency band with a very high directed gain and radiation efficiency.

Le travail de thèse a été réalisée dans le cadre du projet ANR «Stick’It» visant à développer de nouvelles technologies peu coûteuses et innovantes dédiées à la conception de composants radiofréquences (RF) 2D, 2,5D et 3D, notamment des antennes imprimées sur des matériaux conformes. Les applications ciblées sont principalement des appareils de réseaux domestique, tels que les décodeurs, dont les formes et les dimensions sont très variées. Par conséquent, il est nécessaire de concevoir des antennes sur des substrats souples.Selon nos besoins pour un matériau de substrat flexible, peu coûteux, avec de bonnes propriétés RF, la capacité de recyclage et en particulier la capacité à fabriquer des structures 3D, après avoir étudié différents matériaux diélectriques pour l’électronique flexible, le papier s'est trouvé le plus adapté.Les travaux de cette thèse se sont déroulés en trois phases.Dans la première phase, c'était l'étude des méthodes de caractérisation des matériaux pour obtenir leurs propriétés électromagnétiques. Après l'analyse, la méthode de perturbation utilisant une cavité cylindrique a été choisie pour la caractérisation du papier. Les premiers résultats de ce processus ont été vérifiés en réalisant et en testant des antennes simples telles que des monopoles alimentés par CPW sur du papier et du PET. Ensuite, la mesure du papier E4D a été effectuée avec 50 échantillons découpés dans différentes feuilles de papier E4D de trois épaisseurs différentes, 104 m, 210 m et 387 m. Les résultats ont été analysés statistiquement et ont donné r = 3.184, tan = 0.092. Les dispersions des résultats mesurés à 2,5 GHz sont 0.25% pour r et 0.26% pour tan. Ces résultats ont été utilisés pour la phase suivante.Au cours de la deuxième phase, les antennes différentes ont été conçues sur le papier E4D d'épaisseur 0,104 mm et 0,21 mm, notamment des IFA, des antennes SIW et des antennes monopoles alimentées par une ligne microruban. Les prototypes ont été réalisés à l'aide d'une technique de sérigraphie et testés pour déterminer les propriétés de l'adaptation et les diagrammes de rayonnement.Dans la troisième phase, les antennes proposées ont été étudiées dans des conditions d'emballage réalistes, où un boîtier décodeur était en plastique ABS avec différentes dimensions. Le premier cas concernait deux antennes MIMO placées orthogonalement dans des boîtiers ABS différents, avec un espace suffisant pour que les deux puissent rester plats. Le second cas était une boîte à hauteur limitée, de sorte qu’au moins une des antennes doit être pliée.Ainsi, une étude de l'effet de flexion a été réalisée, tout d'abord avec un simple dipôle droit et un monopole droit sur le papier E4D, puis avec une antenne à large bande proposée dans la seconde phase. L’étude a montré que la flexion n’affecte pas beaucoup l’adaptation de l’antenne sur une large bande de fréquences. Cependant, ses diagrammes de rayonnement tournent dans le plan E avec un angle de rotation dépendant de la position de pliage et de l'angle de flexion.Ensuite, le système MIMO de deux antennes placé orthogonalement dans un boîtier ABS de hauteur limitée, de sorte qu’une antenne doit être pliée et une autre reste plate. Dans tous les cas de système d'antenne MIMO, nous avons obtenu une bonne isolation (> 20 dB) et un coefficient de corrélation (ECC) inférieur à 0,05. / The thesis was carried out within the ANR project « Stick’It » that aimed at developing new, low-cost and innovative technologies devoted to the design of 2D, 2,5D and 3D radiofrequency (RF) components including antennas printed on conformable materials. The targeted applications are primarily home-networking devices such as set-top boxes where their forms and dimensions are widely varied. Therefore, it is necessary to design antennas on flexible substrates.According to our needs for a substrate material that is flexible, low cost, with good RF properties, recycling ability, and especially ability to make 3D structures, after considering various dielectric materials for flexible electronics, paper substrate appeared to be the most suitable for our purpose.The work of this thesis conducted in three phases.In the first phase, it was the study of methods for characterization of materials to obtain their electromagnetic properties. After analysis, the method of perturbation using a cylindrical cavity was chosen for characterization of paper. The first results of this process were verified by realization and testing of simple antennas such as CPW-fed monopoles on paper and PET. Then, the measurement of E4D paper substrate was performed with 50 samples cut from various E4D paper sheets of three different thicknesses, 104 m, 210 m and 387 m. The results were analyzed statistically and gave r = 3.184, tan = 0.092.The dispersions of the results measured at 2.5 GHz are 0.25% for r and 0.26% for tan. These results were used for the next phase.In the second phase, different antennas were designed on 0.104-mm and 0.21-mm thick E4D paper including IFAs, SIW cavity-back antenna and microstrip-fed wideband monopole antennas. The prototypes were realized using screen printing technique and tested for matching property and radiation patterns.In the third phase the proposed antennas were studied in realistic package conditions, where a set-top box was made of ABS plastic with different dimensions. The first case was with two MIMO antennas orthogonally located in different ABS boxes with sufficient space, so that both of them can remain flat. The second case was a box with a restricted height, so that at least one of the antennas needs to be bent.Thus, a study of bending effect was carried out, first of all, with a simple straight dipole and a straight monopole on E4D paper, then with a wideband antenna proposed in the second phase. The study showed, that bending does not much affect the matching of the antenna over a wide frequency band. However, its radiation patterns rotate in the E-plane with a rotation angle depending on the bending location and bending angle.Then, the MIMO system of two antennas placed orthogonally in an ABS box with restricted height so that one antenna needed to be bent and another remained flat. In all cases of MIMO antenna system, we obtained good isolation (>20 dB) and Envelope Correlation Coefficient (ECC) less than 0.05.

Due to high demand for planar structures with low loss, a considerable amount of research has been done to the design of substrate integrated waveguide (SIW) components in the mm-wave and microwave range. SIW has many advantages in comparison to conventional waveguides and microstrip lines, such as compact and planar structure, ease of fabrication, low radiation loss, high power handling ability and low cost which makes it a very promising technology for current and future systems operating in K-band and above. Therefore, all the work presented in this dissertation focuses on SIW technology. Five di erent antenna systems are proposed to verify the advantages of using SIW technology. First, a novel K-band end- re SIW circularly polarized (CP) antenna system on a single layer printed-circuit board is proposed. A high gain SIW H-plane horn and a Vivaldi antenna are developed to produce two orthogonal polarizations in the plane of the substrate. CP antennas have become very popular because of their unique characteristics and their applications in satellites, radars and wireless communications. Second, a K-band front-end system for tracking applications is presented. The circuit comprises an antenna array of two Vivaldi antennas, a frequency-selective power combiner, and two frequency-selective SIW crossovers, which eliminate the need for subsequent ltering. The integration of monopulse systems in planar, printed circuit SIW technology combined with the added bene ts of ltering functions is of great importance to the antennas and propagation community. Third, a phased array antenna system consisting of 24 radiating element is designed as feed system for reflector antennas in radio astronomy applications. A Ku-band antipodal dipole antenna with wide bandwidth, low cross-polarization and wide beamwidth is suggested as the radiating element. Forth, four di erent right-angled power dividers including in-phase and out-of-phase dividers as feed systems for antenna arrays are introduced. TE10 - to - TEq0 mode transducers are used for obtaining two, three, and four output dividers with phase control ability at K- and Ka-band. This feature is practical, for instance, when designing tracking systems since they are employed to obtain controllable phase distributions over the output ports. Fifth, a Ku-band beam steering antenna system which is applicable to use for wireless communications, radar systems, and also 5G applications is proposed. This antenna system uses variable reflection-type phase shifters which electrically steer the beam over a 50-degree scan range. Therefore, the SIW technology's reliability and also promising behavior in the microwave frequency range is proven for di erent applications. / Graduate

In modern military operations the requirements of transmitting large amounts of information have increased substantially during the last decade. This increases the demand for high-capacity radio networks. It is also very important that military decisions are made on recent and correct information and this implies that low and known delays are required. The existing military radio ommunications, within the Swedish army, do not meet the requirements for capacity and delay. We have investigated how the capacity and average delay can be improved in an Ad Hoc network with STDMA by using antenna arrays. The study is based on different antenna combinations consistingof single isotropic antenna element, beam steering and adaptive beamforming. We have also studied how the number of antenna elements, the terrain, and an increased connectivity due to the antenna arrays_affects the performance measurements. The study shows that the capacity is improved with up to 1200%, and the average delays are decreased when using antenna arrays instead of single isotropic antenna elements. Depending on the beamforming combination used the capacity gain and average delay reduction will differ. The way of using the antenna array also affects the capacity gain and average delay. The capacity gain is higher when the antenna array is used not only to suppress and decrease interferences, but also to increase the connectivity. The study also shows that the capacity gain is higher when using more antenna elements for a network with a high number of links, than with fewer. The benefit from antenna arrays is higher in a flat terrain than in a rough.

In this dissertation, not only the antenna and antenna array design techniques for fourth-generation mobile communication system are proposed, but also the specifications related to antenna bio-compatibility are studied. At first, two dual-wideband design techniques suitable to be applied for laptop computer applications for LTE/WWAN and LTE MIMO operations are proposed. The techniques can also be applied to internal tablet computer antennas. The isolation issues of MIMO antenna array of different mobile communication devices, such as laptop computer, tablet computer, and mobile phone, are then discussed. Finally, an analysis of body SAR for tablet computer applications are given and discussed.

This thesis presents the analysis, design, and fabrication of a spherical inverted-F antenna (SIFA). The SIFA consists of a spherically conformal rectangular patch antenna recessed into a quarter section of a metallic sphere. The sphere acts as a ground plane, and a metal strip shorts the patch to the metallic sphere. The SIFA incorporates planar microstrip design into a conformal spherical geometry to better meet the design constraints for integrated wireless sensors. The SIFA extends a well-established technology into a new application space, including microsatellites, mobile sensor networks, and wireless biomedical implants. The complete SIFA design depends on several parameters, several of which parallel planar design variables. A modified transmission line model determines the antenna input impedance based on the sphere's inner and outer radii, the patch length and width, short length and width, and feed position. The SIFA can be tuned to the desired frequency band by choosing the proper outer radius, after which the antenna can be matched by tuning the short characteristics, patch dimensions, and feed position. The fabricated design was chosen to operate at the MICS band (402-405 MHz), a popular band for biomedically implanted devices. An initial design was constructed with Styrofoam (epsilon r approximately equal to 1) and copper tape. Simulation in HFSS corroborates that SIFA operation incorporates the MICS band, with resonant frequency of 404 MHz and 32 MHz (7.9%) bandwidth. The fabricated prototype performs similarly, with a resonant frequency of 407 MHz and 19 (4.7%) MHz bandwidth. Following fabrication, several modifications were implemented to miniaturize the SIFA and introduce additional functionality. Slot loading and dielectric coating were implemented to achieve SIFA miniaturization. Multiple elements were also introduced to achieve dual band operation and beam steering. A miniaturized SIFA was investigated in several biological media, and a lossy coating implemented to maintain impedance match in several different media, with the goal of retaining a matched impedance bandwidth in the MICS band.